1. Field of the Invention
This invention relates, generally, to filter cartridges and more particularly to an improved end cap and tube support design for forming a more secure and reliable seal therebetween.
2. Description of the Prior Art
Filter-type cartridges have been used for a significant period of time. The advantages of these types of cartridges are many, with ease of filter change-out being foremost. However, while their ease of use is a great advantage, it is difficult to economically manufacture high quality cartridges.
These types of cartridges are generally tubular in shape, having an inner and outer core or support with a filtration medium disposed therebetween. The filters may be manufactured so as to have the filtered material enter from either end or both ends, exiting through the side walls of the filter cartridge (or vice versa). The filtration medium itself is generally a corrugated fibrous product or a polymer membrane such as a nylon microporous membrane, which is relatively weak from a structural standpoint. Attempts to make the filtration media more structurally stable have a tendency to decrease the filtration capaity of the medium. Therefore supports adjacent to the filtration medium are obviously necessary.
These cage or support portions, in addition to providing structural protection and support for the filtration medium, also allow the cartridge-type assembly to be subjected to substantial forces external to the material being filtered. These forces may be in the nature of vibration, and, in particular, thermal expansion and contraction during sterilization and use as well as direct shock from adjacent components or during installation.
Throughout all this, it is necessary that the filtration medium be securely positioned between the inner and outer cage. It is equally important that the ends be securely attached at the end of the cage portions. While in most situations appropriate gluing or heat sealing of the end cap to the cage portion is not problematic, this technology is severely restricted in the filter cartridge art. The reasons for these restrictions are that excessive heating or use of adhesives may damage or contaminate the cartridge. Additionally, since many applications are for use in sterile and non-toxic areas, certain glues and adhesives as well as methods of attachment are not acceptable.
Further, any failures or structural integrity problems in the end region will deteriorate this region and may result in separation between the end cap and the cage such that unfiltered material will be mixed with filtered material. This occurrence, in any amount, is unacceptable in all circumstances.
Performing all of the above functions has proven to be even more difficult when manufacturing cost considerations are factored in. However, it has been found that proper interconnection between the end portion of the inner and outer cage and the end cap through proper design obviates separation.
There have been numerous attempts at this type of mechanical fix. One such solution may be found in U.S. Pat. No. 4,521,309 "Filter Cartridge with Castellated Support and Process of Making the Same" issued to Pall on June 4, 1985 and which is incorporated by reference herein. The Pall reference utilizes equally spaced castellated end portions at the end of the cage portions. The castellated configuration allows for the recessed portions to have reentrant sides so as to basically form an inverted triangle with one corner of the triangle being fixed to the end of the cage. However, it has been found that this configuration has a number of drawbacks. There, the inner and outer cages utilize the same castellated configuration. These castellations or "inverted triangles" are made to engage specific complimentary formed areas of the end cap. Therefore, it is inevitable that the castellated portion; the conforming portion in the end cap; or both, must first compress or expand respectively, in order to be mated. Further, due to the relative small surface area of the castellations, adequate bonding between the end caps and either cage is only minimal at best. Therefore, by design, the configuration as utilized in the Pall reference inherently leaves room for movement and separation between the end cap and the cage and still relies heavily on the mechanical bond formed by glue, melting of the materials, or the like, between the end cap and the inner and outer cage. Melting is the preferred method described in Pall and is accomplished by melting the end cap before it is placed onto the cartridge. This is necessary due to the inherent weakness in the Pall design with respect to separating the end cap from the cartridge in the axial direction.